1. Field of the Invention
The present invention relates to a vacuum valve.
2. Description of the Related Art
When a vacuum pump such as a turbo-molecular pump and the like is attached to a vacuum chamber of a vacuum processing device, a vacuum valve is generally interposed.
There is a vacuum valve including an opening portion and a valve plate. In this vacuum valve, an opening degree of the valve plate may be changed to change an area (an open area) of a region where the opening portion is released without being opposed to the valve plate (an open region), by which a conductance of the vacuum valve may be changed. This technique may be used for pressure control inside a vacuum chamber.
A vacuum valve of which opening portion has a circular cross-sectional shape is general, and an edge portion of the valve plate of this vacuum valve generally has a circular arc shape. Combination of the opening portion and the valve plate having the above-described shapes causes a problem that at a point where the valve plate starts to open, the change in the open area with respect to the opening degree of the valve plate is large.
In Patent Literature 1 (JP-A-9-210222), there has been disclosed a valve plate having an outline resulting from off-setting apart of an edge end portion inward, or projecting the same outward, which has improved flow controllability.
However, in the invention described in Patent Literature 1, in order to provide the relevant outline, a thickness in an outer circumferential direction of another edge end portion needs to be made large, and as a result, a size of the valve plate is disadvantageously increased. The increase in size of the valve plate incurs an increase in weight and brings about a harmful effect on high-speed operation of the valve plate.